Sunday, September 02, 2012

I've never liked yogurt. Actually, it wasn't that I didn't like it as much as that I never gave it a chance. Curdled milk?! Yuk!!

Then I got older and the doctor sent me to a dietician, who suggested I eat yogurt. I found that I kind of liked the Yoplait custard style yogurts so I settled on that. Then one day someone had me watch a documentary about high fructose corn syrup, which prompted me to check the ingredients in the Yoplait custard style yogurt I'd been eating. Sure enough...

So I switched to something else, and somewhere along the way took an interest in making my own yogurt.

As it turns out, before too long I was making yogurt that I liked pretty well and that was a hell of a lot cheaper than buying it at the store all the time.

I started out by buying a yogurt maker, which is just a set of seven glass jars and a thing to incubate them in. The instructions were to not touch the thing while it was incubating because you'd cause the stuff not to firm up as well as it would if you left it alone. This did not involve draining off any whey, obviously.

I didn't like that yogurt very much, so I started incubating it in as large a plastic dish as would fit in the yogurt maker, and then draining off some of the whey, adding some Splenda and whipping it with an immersion hand blender kind of like this one. I was draining off about a third of the total volume in whey before adding the Splenda, whipping the stuff and putting it in the jars that came with the yogurt maker.

Then I decided the little yogurt maker didn't make enough yogurt in one batch, so I started looking around for a way to make bigger batches. At about that time, I had also taken an interest in sous vide cooking, but you have to maintain precise temperatures in that process, and the sous vide machines are therefore much more expensive that I could justify spending. Figuring I could make something myself, I checked into various temperature controllers but didn't find any that I thought had a suitable combination of price and precision. Eventually, I found a number of sites where people had used an inexpensive PID temperature controller to achieve the temperature aims of sous vide cooking, and found the PID temperature controller they'd been using at Amazon. I figured I'd take a chance on the thing, and ordered the controller, a thermocouple and a solid-state relay plus a heat sink for it (probably not needed for this small a load).

I have not yet done anything with the sous vide cooking idea, but wound up using the controller to make a yogurt incubator large enough for bigger batches. It's really crude, but it works like a champ. Here are a few pictures.

I did say "crude". That's a cardboard banker's box, a computer fan, some duct tape and a 100 watt halogen light bulb.

The round piece of wood shown below is just something I had laying around on which to mount the power strip and other pieces of this precision, custom-made incubator. The power strip supplies electricity to both the PID controller and to the heater (light bulb). The controller (black box at the right) provides a voltage signal to the solid-state relay (light colored box with the red light on it), which, in turn, operates the light bulb. The thermocouple (that tells the controller what the actual temperature is) is sticking into the box through a hole in the cover, which you can see in the upper right-hand corner of the cardboard box.

Here's a similar view showing the face of the controller. I did say "crude" didn't I?

The thing in the lower right of the picture above is just a switch to isolate the light bulb from the solid-state relay. I don't think it's necessary, but it's harmless enough, and might be a good place to put a temperature limiting safety device of some sort. Nothing wrong with belt and suspenders.

Here's how I make the yogurt. Greek style yogurt, which, as far as I can tell, simply means that you drain off more of the whey.

I dump a gallon of milk into a stainless steel pot and heat it to a boil, stirring constantly. The recipes I see all call for heating the milk to 180 degrees Fahrenheit, but for some reason I decided to boil the milk. Works fine.

I cool the boiled milk in a water bath until the temperature drops to about 115 or 120 degrees. No hotter or I might kill the yogurt culture. Maybe not, I don't know, the whole process seems very forgiving.

I mix in some yogurt from the previous batch as a starter to introduce the bacteria that do the actual work. It doesn't much matter how much starter goes in. Thoroughly stir in the starter and stick the covered pot into the incubator, with the controller set to 115 degrees. Like this:

I usually let it incubate for about 12 hours at 115 degrees F, then drain off about a quart and a half of whey, add a cup and a half of granulated Splenda (or the generic equivalent), whip it, whip it good, pour it into suitable individual containers and into the fridge.

As I already mentioned, the whole process is pretty forgiving and open to experimentation. I made one small batch with some sugar-free smooth orange-flavored Metamucil mixed in at the last minute. Turned out pretty good, actually, although my wife won't eat it. It thickened up the yogurt a bit more than it would be on its own, and it tasted OK. One time I added some vanilla extract, which was OK but my wife didn't like it. She, like I, has never been a yogurt eater, but she likes the stuff I make as long as I don't fiddle with it beyond the Splenda.

I've found the easiest way to drain off the proper amount of whey is to dump the stuff just out of the incubator into a large-enough container lined with sack cloth, or some other light fabric such as a large handkerchief (wash it first!), then hang the yogurt in the cloth over the dish until sufficient whey (about one third of the total volume), has drained off. At that point, take the curds from the sack cloth to a dish, add the Splenda (or whatever you like), and whip it. Whip it good.

Fun activity, cheaper than store bought and just as good if not better. Now if I could find a good use for the whey...

Some final thoughts...

Incandescent light bulbs are not intended to be cycled on and off continuously, and I've expected this bulb to fail for a long time. It keeps on working, though, which may be because the controller cycles it quickly enough to avoid the worst of the thermal shock. Obviously there is a great temperature difference between incandescence and dark, but at least the filament doesn't get cold during the off portion of the duty cycle. Some of the unexpected longevity is probably because I used a halogen bulb, in which tungsten that boils off of the incandescent filament is mostly re-deposited on that filament instead of on the bulb's glass (or so I understand). Eventually, though, a different heater is probably in order.

A cardboard box is probably not the safest thing to use for this purpose. It's safe enough, but one of these days I'll find something more suitable.

The controller, solid state relay and such should probably be enclosed. As it is, there's no shock hazard (well, not much), but UL certainly wouldn't approve what I've done. I'll do something about that eventually.

I learned today that if the thermocouple comes out of the box, it's going to get quite a bit hotter than intended inside the incubator. That won't happen again.

Learning to use the PID temperature controller actually required reading the manual, and reading the correct manual.